1. Field of the Invention
The present invention relates to an electronic apparatus and a controlling method for the same, and more particularly, to an electronic apparatus having functions of calculating a remaining usable time for the electronic apparatus based on a remaining capacity of a battery pack and for displaying a result of the calculation, and a controlling method for the electronic apparatus.
2. Description of the Related Art
A conventional video camera includes a microcomputer and a current detecting circuit in a battery pack, with which a charge capacity is calculated by accumulating charge-discharge current of a battery cell, remaining capacity information on the battery cell is transmitted to the video camera, and a remaining usable time is displayed on the video camera. Some of the conventional video cameras calculate and display the usable time for each of a plurality of operation modes such as a camera mode and a reproducing mode (for example, refer to Japanese Laid-Open Patent Publication (Kokai) No. H09-297166).
However, the above conventional video camera suffers from a problem that a correct remaining usable time cannot be displayed with an unexpected load induced, for example, when an external apparatus such as a video light is connected to the video camera.
In the conventional video camera, a power may be delivered from the battery pack through a DC/DC converter. In this case, a load on the battery cell in the battery pack is close to a constant power. When a typical lithium-ion cell used for the battery pack is discharged at a constant power, as shown in FIG. 6, the amount of discharged current is smaller under a high voltage condition at the beginning of discharge than under a low voltage condition at the end of discharge. At this time, if the remaining usable time is calculated from the discharged current and the remaining capacity of the battery pack, the calculated remaining usable time becomes longer than the correct remaining usable time since the discharged current is smaller at the beginning of discharge.